Lecture 8: Natural Selection and Adaptation

Question 1

Fitness

Answer 1

relative genetic contribution of individuals to next generation as a result of differences in viability and fertility

Question 2

selective advantage

Answer 2

individuals more adapted to (higher fitness) environment have advantage

Question 3

Adaptation

Answer 3

• any trait that contributes to fitness by making an organism better able to survive or reproduce in a given environment (noun)
• evolutionary process that leads to the origin and maintenance of such traits (verb)

Question 4

Artificial Selection

Answer 4

domesticated plants and animals; selection experiments in genetics
(human interference)

Question 5

How large do selective advantages have to be before they are favoured and spread?

Answer 5

Even a 1% or less selective advantage will be favoured.

Question 6

Stabilizing selection

Answer 6

Changes variance of the trait. Selection favours the mean.

ex. human birth weight.

Question 7

Directional selection

Answer 7

Changes the mean of the trait. Selection favours on of the extremes.
ex. beak size in Galapagos finches after drought

Question 8

Disruptive selection

Answer 8

Changes variance of the trait. Both extremes are favoured and mean is not at all. Leads to character divergence and sometimes speciation.
ex. African finches, large beaks are favoured for hard seeds, small beaks are favoured for soft seeds. Mean is selected against.

Question 9

How do we study adaptation?

Answer 9

• allele frequency or trait correlations with environment over space and time
• studies of genomic diversity (target gene shows unusual patterns of genetic diversity indicative of natural selection)
• manipulative field experiments

Question 10

Peppered Moth (UK)

Answer 10

• showed evolution in response to pollution
• light variant was homozygous recessive but at much higher frequency until the industrial revolution covered everything in coal and they became suddenly way more visible to predators

Question 11

Heavy metal tolerance in plants

Answer 11

tolerant genotypes invade mine tailings from nearby pastures, gene flow between pasture and mine restricted because of different flowering times. Has evolved independently in many different areas in Ontario. Ability to tolerate has a cost which is why plants in the pasture do not have same ability (perhaps it would affect their ability to absorb nutrients and minerals, similar to balance between UV radiation and Vit D synthesis)

Question 12

crypsis

Answer 12

the ability of an animal to avoid observation and detection by other animals.

Question 13

Why would the allele for G6PD have a selective advantage?

Answer 13

In areas where malaria is present, the allele which makes one malaria resistant would be beneficial. If malaria isn’t present the gene is not selected for because anemia is costly.

Question 14

Richard Lenski

Answer 14

Known for 20 year long study with E. coli (40 000 generations of evolution). He started with one strain of E. coli, grew 12 populations each on low glucose (citrate) medium and at the 33 000 gen. , mutation happened that allowed them to thrive on citrate. Similar parallel mutations arose in the distinct populations of E. coli.